The present invention relates to a thermal-resistance variable heat sink structure and to a method of using the same. Particularly, the present invention relates to a technique of screening chips.
In large-scale computers or the like, the so-called chip set where plural LSIs (large-scale integrated circuits) are mounted on the same board has generally used to realize predetermined functions. When the function of an LSI is realized, a high-dense chip results in larger power consumption, whereas a low-dense chip results in lower power consumption.
The high-dense chip consumes larger power, thus generating a larger heat amount. For that reason, a heat sink or a cooling fan is attached to the chip to cool the chip, thus stabilizing the performance of the chip itself.
In the shipment of a chip, whether or not the chip achieves predetermined functions is judged using an automatic IC (integrated circuit) tester. Thus, the screening is carried out to sort defective items and accepted items.
Conventionally, chips are basically subjected to the DC screening in which a constant voltage is applied to them before the shipment. However, the qualities of chips are not often maintained. Hence, the AC screening (reinforced screening) is required to increase the power consumption after chips are mounted on a board. In this case, the AC screening can be realized by modifying the heat sink structure. However, this approach has not been practically because of a large number of man-hours.
The present invention is made to solve the above-mentioned problems. An object of the present invention is to provide a thermal-resistance variable heat sink structure that can improve the quality at a working time and can change the shape of a heat sink and reduce the number of steps for attaching or detaching.
Another object of the present invention is to provide the method of using the above-mentioned heat sink structure.
According to the present invention, a thermal-resistance variable heat sink structure comprises a thermal resistance adjuster disposed on a heat sink to cool an integrated circuit device. The thermal resistance adjuster has a thermal resistance equal to or more than that of a material for the heat sink.
Moreover, in a method of using a thermal-resistance variable heat sink structure, according to the present invention, the method comprises the steps of using a thermal resistance adjuster in a factory inspection and then disassembling the thermal resistance adjuster in shipment. The thermal resistance adjuster is disposed on a heat sink to cool an integrated circuit device and is formed of a material having a thermal resistance equal to or more than that of the heat sink.
That is, in the thermal-resistance variable heat sink structure of the present invention, a thermal resistance adjuster (comb-like plate), which utilizes air blocking function, is mounted on a slit-like heat sink to realize a low thermal resistance. The thermal resistance adjuster is formed of a material having a thermal resistance larger than that of the heat sink.
In the heat sink structure, a thermal-resistance variable heat sink is used for low-power LSIs among many LSIs mounted on a board. Thus, the screening is performed by accelerating the premature failure while the junction temperature of the low-power LSI is set to the same value as that of a high-power LSI.
That approach allows the ambient temperature about LSIs mounted on a board to be fixed. Hence, the screening can be carried out with increased junction temperatures of low power LSIs with low integration density.
Moreover, products that are nearly defective can be initially rejected at the fabrication step. As a result, the quality of an LSI at an operational time can be improved. It is possible to change the structure of a heat sink and to reduce the number of attaching and detaching steps.